The invention is directed to a process for (partial) exhaust gas recirculation into an air intake region of a motor vehicle internal combustion engine in which a mixture of exhaust gas and in-flowing air, adjustable by a regulator, is fed to the engine. The mass of air is determined by a flow rate sensor, and a fuel amount is fed as a function of the air mass through-flow rate, taking into consideration a performance specification signal. The invention also includes a device for carrying out the process.
From German Patent DE 42 11 851 C2 a process is known for determining cylinder air flow rate in connection with an electronic engine control system of an internal combustion engine with an exhaust gas recirculation device. It relates to a process for controlling an internal combustion engine with an exhaust gas recirculation (AGR) system for regulating toxic emissions, wherein an exact value for the aspirated air flow rate (cylinder air flow rate) of the gas is determined as it is actually introduced into an engine cylinder during the active state of the AGR system. This is necessary for good engine control. Furthermore, a process is described for the exact determination of the amount of fuel to be injected, wherein the transport delay of the fuel is considered in the suction nozzles.
For the purpose of control or regulation of toxic gas emissions and to save fuel, internal combustion engines for motor vehicles use electronic control systems, which hold the air/fuel mixing ratio to a target value essentially in the entire engine operation region. In order to control the air/fuel mixing ratio with great accuracy, the cylinder air flow rate of the gas actually sucked into an engine cylinder is determined exactly, and the requisite fuel flow is determined on the basis of the values for the aspirated air flow rate and the target air/fuel ratio. The relatively complex determination of the recirculated exhaust gas flow rate appears problematic here.
Furthermore, eliminating toxic components in exhaust gases of internal combustion engines, in order to keep the ambient air as clean as possible, is known from German published patent application DE-OS 22 35 568. The toxic components consist essentially of carbon monoxide and combusted hydrocarbons and nitrogen oxides. For eliminating carbon monoxide and combusted hydrocarbons, thermal and catalytic afterburning processes were developed. Furthermore, the possibility is pursued of achieving a reduction of nitrogen oxide emissions by recirculation of a portion of the combustion exhaust gases into the combustion chamber (exhaust gas recirculation). By recirculating a portion of the exhaust gases consisting essentially of inert gases, the peak combustion temperature in the main combustion chamber is so reduced that the emission of nitrogen oxides is decisively reduced. For exhaust gas recirculation, generally up to 15 percent of the total amount of exhaust gas is withdrawn, which is taken at any point in the exhaust gas conduit.
From U.S. Pat. No. 4,462,376 a process is known for determining and regulating an exhaust gas recirculation rate in internal combustion engines (diesel engines), wherein an adjustment link in the exhaust gas recirculation chain is adjusted by a regulator, in order to obtain a precise regulation of the amount of exhaust gas which is fed into the air intake zone of the engine. The regulator is provided with the exhaust gas temperature, which at a specified time serves as a load signal for the engine. The reference signal of the regulator is then either a current value of the exhaust gas recirculation rate, which is determined by devices for effective temperature measurement in the intake region of the engine, or a specified temperature difference is determined, which is determined by devices for measuring the aspirated air amount at a given time. The problem is seen here that an optimal adjustment of the operating point, which would lead to a low impact on the environment, is not possible without further measures.
The invention has for an object the attainment, from determined parameters of the motor vehicle internal combustion engine, of an optimization of the engine operation with regard to efficiency and low environmental impact, wherein the parameters should be determined in the simplest manner possible.
The objective is accomplished according to the process of the invention in that, exhaust gas exiting the engine is fed to a further flow rate sensor wherein, from the determined flow rates of aspirated air and recirculated exhaust gas, an actual value signal (X, X1, X2) is formed and compared with a target value signal (W) for an optimal operating point of the engine, wherein a regulation deviation of the actual value signal leads to an adjustment signal which intervenes in the exhaust gas recirculation with the aid of an adjustment member.
In an advantageous embodiment of the process, exhaust gas exiting from the engine is cleaned of combustion products before it is cooled. Furthermore, especially with larger engines (e.g., for trucks), a cooling of the exhaust gas is provided, preferably to a temperature in a range of about 70xc2x0 C. to 300xc2x0 C. With the aid of an adjustment signal (Y, Y1), at least one adjustment member in the exhaust gas recirculation is controlled, which is preferably constructed as a contollable valve.
In a preferred embodiment of the process, the target value signal (W) is derived from a performance specification signal (e.g., gas pedal) and at least one parameter of the engine. As a parameter, at least one signal is provided which is formed from the exhaust gas temperature or rotational speed, as well as the mass of flowing air. Here, at least one signal, as an engine parameter, is compared with a reference signal through difference value formation, wherein exceeding a specified difference value leads to an adjustment signal (Y, Y1, Y2).
While the adjustment signals Y, Y1 directly intervene in the exhaust gas recirculation, preferably by means of a controllable valve, adjustment signal Y2 acts upon an adjustment member, which is located in the intake region of the internal combustion engine, into which a mixture of in-flowing air and partially recirculated exhaust gas flows in.
Preferably, adjustment signal Y2 acts upon a compressor in the intake region of the internal combustion engine wherein, with the aid of adjustment signal Y2, the adjustment of the blade angles is undertaken according to the xe2x80x9cprinciple of variable blade shape in compressors.xe2x80x9d It is, however, also possible to have adjustment signal Y2 act upon a valve arrangement.
Preferably, the signals are converted into digital signals by means of an analog/digital converter and stored. Subsequently, a comparison of the stored values with digital reference values is undertaken.
In a preferred embodiment of the process, at least two heating resistors maintained at constant temperature in the flow rate sensor are successively flowed past for measuring the flowing mass of the exhaust gas. Here, the heating resistors are respectively flowed through by an adjustable current (I1, I2). From the strength of the currents (I1, I2) a signal is formed for the flowing mass and its direction.
Furthermore, in an advantageous embodiment of the process, the resulting flow of the flowing mass is determined from at least one pulsating current I1 and I2 by alternating multiplication of the current amplitudes with +1 and xe2x88x921 and a subsequent difference value formation.
The objective is achieved according to a device of the invention for (partial) exhaust gas recirculation from an exit region of a motor vehicle internal combustion engine into an air intake region, in which a mixture of exhaust gas and in-flowing air, adjustable by regulation, is feedable into the engine. For determining the mass of air, a flow rate sensor is provided, and a fuel amount is adjustable as a function of the air mass through-flow rate, taking into consideration a performance specification signal. The exit region is connected with an intake region of the internal combustion engine via a flow channel for exhaust gas recirculation, which has at least one temperature sensor, a controllable valve as adjustment member, and an additional flow rate sensor.
In one embodiment of the device expedient for practice, an exhaust gas-cooling device is arranged in the flow conduit for the exhaust gas recirculation between the exit region and the additional flow rate sensor.
In a first advantageous embodiment of the device, the flow rate sensor has at least one temperature-dependent measurement resistor with rapid response time. Advantageously, the measurement resistor is constructed as a thin layer or thick layer element on the measuring technology basis of platinum or a platinum group metal.
In the first embodiment of the invention, the flow rate sensor has at least one measurement resistor and at least one heating resistor, wherein the resistors are constructed respectively in microsystem technology. The heating resistor(s) are provided for operation in the temperature range of about 350 to 750xc2x0 C.
A flow rate sensor with a measurement resistor with short response time and a rapid microheater is known, for example, from European published patent application EP 0 964 230 A2.
In a second advantageous embodiment of the invention, the flow rate sensor has at least two rapid microheaters or heating resistors, which are operated at well-defined, fixed, excess temperatures, for example 450xc2x0 C. and 550xc2x0 C. The temperatures are selected such that depositing soot is constantly combusted by pyrolysis, and the microheaters consequently always remain clean. A rapid control electronics unit feeds the heater with current, such that its temperatures are held constant. The evaluation of the heating currents permits an unambiguous inference as to both the flow rate and the mass temperature. By using platinum heating elements, which can be manufactured in thin as well as thick layer technology, heating temperatures from 350xc2x0 C. to 750xc2x0 C. can be set using the well-defined resistance temperature characteristic curves of platinum.
A basic advantage of the second embodiment (two heating resistors) is that practically no sooting takes place on the heating resistors, so that they are always operated with optimal measurement characteristics.
The heating and measurement resistors are advantageously constructed in at least two strip conductors on a plate-like membrane, preferably of an electrically insulating and heat resistant material, such as ceramic.